How To Construct A Gravity Battery

To set up a gravity battery use about 3 1/2
pounds of bluestone, or enough to cover
the copper element 1 inch. Pour in water
sufficient to cover the zinc one-half (1/2)
inch, short circuit for three hours and the
battery is ready for use. If desired for
use immediately do not short circuit, but
add five or six ounces of "zinc sulphate."

Keep the dividing line X between the
blue and white solutions about one-half
inch below the bottom of the zinc. If too
low, siphon off some of the white liquid
and add the same amount of water, but do
not agitate or mix the two solutions.

This type of battery will give about 0.9
of a volt, but only a fraction of an ampere.
It is used for burglar alarm and closed circuit
telegraph work very extensively.

Many amateur electricians and some professionals
have undoubtedly had considerable
trouble with gravity batteries. They
follow directions carefully and then fail to
get good results. The usual trouble is not
with the battery itself, but with the circuit.
A gravity battery is suitable only for a circuit
which is normally closed, it is therefore
undesirable for "electric bells," "induction
coils" and all other open circuit apparatus
requiring fairly strong current.

The circuit should also have a high resistance.
This makes it impractical for running
fan motors, as the motor would have
to be wound with fine wire. And it would
then require a large number of batteries
to give a sufficiently high voltage.